The present invention relates to connectors for connecting stabilizers and bits and more particularly to connecting eccentric adjustable blade stabilizers to bi-center bits having eccentric reamers.
In the drilling of oil and gas wells, concentric casing strings are installed and cemented in the borehole as drilling progresses to increasing depths. In supporting additional casing strings within the previously run strings, the annular space around the newly installed casing string is limited. Further, as successive smaller diameter casings are suspended within the well, the flow area for the production of oil and gas is reduced. To increase the annular area for the cementing operation and to increase the production flow area, it has become common to drill a larger diameter new borehole below the terminal end of the previously installed casing string and existing cased borehole so as to permit the installation of a larger diameter casing string which could not otherwise have been installed in a smaller borehole. By drilling the new borehole with a larger diameter than the inside diameter of the existing cased borehole, a greater annular area is provided for the cementing operation and a subsequently suspended new casing string with a larger inner diameter provides a larger flow area for the production of oil and gas.
Various methods have been devised for passing a drilling assembly through the existing cased borehole and permitting the drilling assembly to drill a larger diameter new borehole than the inside diameter of the upper existing cased borehole. One such method includes the use of a winged reamer disposed above a conventional bit and another method includes the use of a bi-center bit. Various types of bi-center bits are manufactured by Diamond Products International, Inc. of Houston, Tex. See the Diamond Products International brochure incorporated herein by reference.
A bi-center bit is a combination reamer and pilot bit. The pilot bit is disposed on the downstream end of the drilling assembly with the reamer disposed upstream of the pilot bit. The pilot bit drills a pilot borehole on center in the desired trajectory of the well path and then the eccentric reamer follows the pilot bit reaming the pilot borehole to the desired diameter for the new borehole. The diameter of the pilot bit is made as large as possible for stability and yet still be able to pass through the existing cased borehole and allow the bi-center bit to drill a borehole that is approximately 15% larger than the diameter of the existing cased borehole.
The drilling assembly must have a pass-through diameter which will allow the assembly to pass down through the existing cased borehole and then pass back up the new borehole and existing cased borehole upon completion of drilling. The reamer section of the bi-center bit is eccentric and typically the bi-center bit is used with a stabilizer having a fixed eccentric blade. The stabilizer is located above the reamer section of the bi-center bit such that they must pass together through the upper existing cased borehole. The stabilizer and bi-center bit must be sized so that the drilling assembly has a pass-through diameter which will allow the drilling assembly to pass through the existing cased borehole without excessive wedging.
Typically a fixed blade stabilizer is mounted above the bit on the drilling assembly. The fixed blade stabilizer includes a plurality of blades azimuthally spaced around the circumference of the housing of the stabilizer with the outer edges of the blades being concentric and adapted to contact the wall of the existing cased borehole. The stabilizer housing has approximately the same outside diameter as the bi-center bit. Obviously, the fixed blade stabilizer must have a diameter which is smaller than the inside diameter of the upper existing cased borehole, i.e. pass-through diameter. In fact the fixed blade stabilizer must have a diameter which is equal to or less than outside diameter of the pilot bit of the bi-center bit. Therefore, it can be appreciated that the blades of the fixed blade stabilizer will not all simultaneously contact the wall of the new borehole since the new borehole will have a larger diameter than that of the upper existing cased borehole.
An adjustable concentric blade stabilizer may be used on the drilling assembly. The adjustable stabilizer allows the blades to be collapsed into the stabilizer housing as the drilling assembly passes through the upper existing cased borehole and then expanded within the new larger diameter borehole whereby the stabilizer blades engage the wall of the new borehole to enhance the stabilizer's ability to keep the pilot bit center line in line with the center line of the borehole. One type of adjustable concentric stabilizer is manufactured by Halliburton, Houston, Tex. and is described in U.S. Pat. Nos. 5,318,137; 5,318,138; and 5,332,048, all hereby incorporated herein by reference. Another type of adjustable concentric stabilizer is manufactured by Anderguage U.S.A., Inc., Spring, Tex. See Andergauge World Oil article and brochure incorporated herein by reference.
It is preferred that the stabilizer be only two or three feet above the bi-center bit to ensure that the pilot bit drills on center. Having the stabilizer near the bi-center bit is preferred because not only does the stabilizer maintain the pilot bit on center, but the stabilizer also provides a fulcrum for the drilling assembly to direct the drilling direction of the bit.
The present invention overcomes the deficiencies of the prior art.